The present invention relates to an alphanumerical keyboard, which includes a plurality of numeral keys and function keys. The invention is primarily applicable to keyboards of limited size and having a limited number of keys, and then particularly with keyboards for hand-held computers and mobile telephones.
A number of alphanumerical keyboards are known to the art which function in a numeral mode and in an alphabet mode when appropriate keys are depressed; see for instance U.S. Pat. Nos. 4,549,279, 4,994,992, 5,117,455 and 5,339,358 in this regard. The first two of the aforesaid U.S.-patent specifications also teach a keyboard in which simultaneous depression of up to four mutually adjacent keys is utilized to create as many functions as possible with as few keys as possible. Although a keyboard of this construction is compact, it is also difficult to grasp, i.e. is not easily managed and therewith not particularly user friendly. The two latter U.S.-patent specifications mentioned above teach keyboards in which pairs of mutually adjacent keys are used to generate certain letters or alpha-characters when the keys of said pairs are depressed one after the other.
The object of the present invention is to provide an alphanumerical keyboard of limited size and having a limited number of keys which is both user friendly and which will enable numerals and alpha-characters to be generated alternately by pressing one or more keys with only one finger of one hand and without using a shift key.
These objects are achieved in accordance with the invention with an alphanumerical keyboard of the aforedefined kind which is characterized in that the keyboard is programmed so that when two mutually adjacent keys are depressed simultaneously one alpha-character will always be generated while a numeral will always be generated when depressing only one numeral key. Because numerals are always generated by depressing only one key and letters are generated by depressing two mutually adjacent keys simultaneously, a user will find it very easy to separate these functions and to quickly key-indata that contains both numerals and letters or alpha-characters. Because the keys are separated from one another, there is also less risk of a user unintentionally depressing two adjacent keys simultaneously.
According to one preferred embodiment of the invention, the numerals and the alpha-characters are generated when a single key or two keys return from a depressed position, and wherein depression of one key will activate search means, or scanning means, which investigate whether an adjacent key is depressed over a given time duration.